Powered wheelchairs often have six wheels including a pair of center wheels, a pair of rear wheels, and a pair of front wheels. Typically, one pair of wheels is driven by, and directly connected to, a drive. The front wheels may be suspended above the ground plane on which the wheelchair rests or in contact with the ground. Typically, wheels that are spaced apart from the ground surface, or configured to only lightly contact the ground surface, are fixed except for the capability of turning about their axes of rotation; such wheels are referred to herein as “fixed wheels.” Wheels that are configured to ride on the ground surface during normal operation typically have the capability to swivel about a vertical axis; such wheels are referred to herein as “casters.”
Wheelchairs that employ fixed wheels often employ springs to suspend the fixed wheels above the ground at the end of forward extending arms. The fixed wheels are the first part of the wheelchair that contact a curb, and the fixed wheels are often configured to ride over a curb.
Wheelchairs that employ casters often are disposed on forward-extending arms that are coupled to the frame at a pivot. Some wheelchairs, such as those employing an Active-Track™ suspension, available on some powered wheelchairs from Pride Mobility Products Corporation, have pivoting front caster arms that raise or are upwardly biased in response to wheelchair acceleration or motor torque to enhance the capability of the wheelchair to climb curbs. Pivotable front caster arms typically employ biasing springs to provide a downward force that is balanced against the drive's capability to raise the casters for ascending a curb and that urges the casters downward to contact the lower ground surface while descending a curb.
Wheelchairs typically have a frame onto which loads from the passenger and the wheelchair's batteries are applied. To properly distribute the load between the center wheels and the rear casters (and where applicable the front casters) and to enhance stability of the wheelchair, loads from the batteries and passenger typically are applied between the axis of rotation of the center wheels and the rear casters, especially where the center wheels are the drive wheels. Often, the batteries are located such that the center of gravity of the batteries is near, but rearward of, the center drive wheels or in general near the center of the wheelchair. To accommodate the battery location, the drive for each drive wheel typically includes a longitudinally oriented (that is, oriented parallel to the axis of straight-ahead movement of the wheelchair) motor and a right-angle gearbox. An exception to such drive and battery configuration is shown in U.S. Pat. No. 5,964,473 (“Degonda”), which discloses a transversely oriented motor that splits the battery compartment.
Because the conventional location of the battery compartment is at least partly underneath the passenger chair, the chair must be removed to access the batteries.
Furthermore, there is a general need for wheelchair configurations that are simple and inexpensive, yet are effective in climbing obstacles such as curbs.